The present invention is directed to an optical four-gate coupler which has a pair of input coupling multimode optical fibers and a pair of output coupling multimode fibers in which the planar end faces of the four fibers abut one another in an axial offset fashion.
Optical four-gate couplers which have a pair of input multimode optical fibers connected to a pair of output fibers are known and an example is disclosed by H. H. Witte and V. Kulich "Planar Input-Output Couplers in Thick-Film Technology for Multimode Optical Fibers", Siemens Forsch.-u-Entwickl.-Ber., Vol. 8, 1979, No. 3, pages 141-143. In the case of known couplers, the diameter of all the optical fibers are of equal size and as a consequence the degree of input coupling is equal to the degree of output coupling. If such couplers are employed in optical data buses with T-network structures, this results in an input coupling loss increasing linearly with the number of subscribers.